An input-output approach for giant atom scatterings beyond the dipole approximation

TL;DR

This paper develops a modified input-output approach to analyze electromagnetic scattering of giant atoms, capturing Fano-type spectra and physical parameters beyond the dipole approximation.

Contribution

It introduces a new method that extends the input-output approach to giant atoms, explaining complex scattering phenomena beyond previous models.

Findings

Successfully explains Fano-type scattering spectra in giant atoms.

Extracts physical parameters like energy dissipation and coupling strength.

Suggests potential for high-performance quantum optical devices.

Abstract

A giant atom is an artificial matter configuration whose spatial scale is comparable to the wavelength of the interacting electromagnetic wave, such that the usual electric-dipole approximation is no longer valid. As a consequence, certain quasi-direct scattering channels for the electromagnetic wave can arise. Given that the well-known input-output approach can only work for the usual point scattering configuration, wherein the electric-dipole approximation is well satisfied, here we develop a modified input-output approach, wherein an additional low-Q cavity channel is introduced, to treat the electromagnetic scattering problem of a giant atom. We demonstrate that, beyond the multiple coupling-point model used widely in recent publications, the present approach can well explain the Fano-type scattering spectra observed generically and extract certain physical parameters, including the energy dissipation parameter of a two-level giant atom and its coupling strength with the scattered electromagnetic wave. Consequently, we argue that various high-performance optical quantum devices, typically the giant-atom-based optical quantum switches, can be generated by engineering the Fano-type scatterings of giant atoms.